The present invention pertains to reflection minimized photonic crystals and to devices utilizing such materials.
Typical 2-dimensional photonic crystals consist of a dielectric slab having periodic dielectric regions present in the form of air holes or dielectric rods in air. For purposes of light propagation, infinite thickness can be assumed. Refractive indices less than 1 and even refractive indices having negative values can be engineered in various photonic crystals.
When there is a mismatch between the refractive index of the photonic crystal and the refractive index of an associated background media or air, certain amounts of light reflection can occur. Light reflection occurs when light incident from a background or air region to the photonic crystal lacks unity of absolute refractive index. In situations where the absolute refractive index is much less than 1 or much larger than 1, this disunity results in large amounts reflection. This limits the transmissive effectiveness of the photonic crystal.
In beam steering applications utilizing superprism effects, large refraction angles are achieved by engineering photonic crystal structures with extremely small absolute refractive indices at the crystal interface. This enables significant refraction corresponding to small variations in the incident angle as light enters the crystal structure. The need for ever smaller absolute refractive indices as well as negative refractive indices increases as the need for devices with ever wider beam steering angles increases.
Such small absolute refractive index values result in large amounts of reflection at the interface between the photonic crystal and air or the background media. Such reflection phenomena limit the effectiveness of the photonic crystal structure and any associated device, such as a beam steering structure and super prism lenses.
It would be desirable to provide a reflection minimized photonic crystal structure. Various methods have been proposed, but the need for effective reflection minimization remains. Devices utilizing photonic crystals with effective reflection minimization would find application in numerous configurations including but not limited to superprism lenses and beam steering devices such as near vertical-incidence thin structures.